Despite an absence of data demonstrating efficacy as an antiplatelet agent, rectal aspirin is currently being administered to hospitalized patients with acute myocardial ischemic syndromes who are unconscious or who cannot tolerate oral medications due to emesis or pathological conditions of the gastrointestinal tract. This randomized, double-blinded, placebo-controlled, complete crossover study, is designed to compare the onset and magnitude of effects of ex-vivo platelet aggregation and suppression of thromboxane B2 production, between oral and rectal aspirin (325 mg tablet versus 300 mg suppository) in healthy middle-aged volunteers.